Speakers
Description
Cavity-based x-ray free electron lasers (CBXFELs) such as the x-ray regenerative amplifier FEL (XRAFEL) and the XFEL oscillator (XFELO) have been proposed to produce stable, fully-coherent, hard x-ray unreachable with the current XFELs. XRAFEL approach employs high-current, short-bunch electron beams to support a high-gain FEL process, resulting in substantial pulse energy. On the other hand, XFELO utilizes a low-gain FEL process with long bunch length, low current electron beams and achieves extremely narrow pulse bandwidths. Here we introduce the novel concept of staging, which combines the strength of XRAFEL and XFELO to generate hard X-ray pulses with very narrow bandwidth while maintaining high pulse energy. We first kick-start the cavity with high-current electron beams to obtain high intra-cavity power. After that, we gradually decrease the beam current and increase the bunch length until it matches the recirculated pulse length. Leveraging post-saturation tapering, the FEL power can be continuously boosted. A case study based on LCLS-II HE and CBXFEL project parameters demonstrates generating 20keV hard x-ray pulses with mJ energy and sub-10 meV bandwidths.
